Actress Shannen Doherty just broadcast some good news about her journey. (Photo: VALERIE MACON/AFP/Getty Images)

Actress Shannen Doherty announced that her breast cancer (which was first diagnosed in March 2015) is in remission and on Instagram told her followers: "Moments. They happen. Today was and is a moment. What does remission mean? I heard that word and have no idea how to react. Good news? YES. Overwhelming. YES. Now more waiting." Here's a tweet of hers:

Moments. They happen. Today was and is a moment. What does remission me? I heard that word and… https://t.co/psg0984OGh

Yes, it is very good news for the former Heathers, Beverly Hills, 90210 and Charmed star. But what exactly does remission mean? It doesn't mean that the 46-year-old is necessarily done with treatment. She's certainly not done with visits to the doctor. And it doesn't mean that she's cured. Partial remission says that the cancer has been reduced in size but is still detectable. In this situation, doctors may stop treatment for a while and just closely observe the patient to ensure that the situation does not get worse. Imagine doctors "fencing off" the cancer and continuing to circle around it to make sure that nothing gets past the fences. By contrast, complete remission implies that doctors can find no evidence of disease (NED) based on their laboratory tests, imaging, scans, exams and other methods. But no test or exam is perfect or can detect every single cancer cell in your body. That's why close follow-up is necessary. In fact, even when the patient is in complete remission, doctors may give more treatment in attempts to eliminate any undetectable cancer cells. Presumably, Doherty is in complete remission.

After complete remission is declared, cancer recurrence happens if and when the cancer becomes detectable again. Note that this could be quite different from "return." Return would imply that something has completely left and is now back again. (For example, Beverly Hills, 90210 disappeared from the primetime Fox lineup on May 2000. Some of the characters returned in subsequent spinoffs such as Melrose Place in July 1992 and 90210 in September 2008). By contrast, recurrence can simply be the recognition that what was always present but previously not noticeable has now become detectable again. (Just like ants or termites still lingering in your house.) In other words, the cancer cells were hiding in the body away from detection and then slowly started multiplying and spreading to the point that the cancer becomes apparent again.

The longer a patient goes without cancer rearing its ugly head again, the greater the likelihood that there are not enough cancer cells left in the body to start trouble again. That's why the risk of recurrence goes down with time. Doctors may classify breast cancer recurrences within five years of initial diagnosis and treatment as "early" and those more than five years after as "late recurrences," but nothing magical happens on day 1,826. Patients don't suddenly become new people at the five-year mark. The five-year mark emerged as a somewhat arbitrary cutoff when researchers were analyzing data on patients to allow them to compare different time periods. Cancer can still recur well beyond the five-year mark...although with each passing day, recurrence becomes less and less likely.

Doherty once authored a book with a title that started with the word "BadAss," but her documenting on social media her breast cancer journey has been quite good, bringing more attention to and awareness and understanding of the disease. Many misconceptions still remain, but her good remission news could mean that she can continue such advocacy for years down the road.

I’ve been in the worlds of business, medicine, and global and public health. And these worlds are a lot more similar and different than you think. Currently, I am an Associate Professor of International Health at the Johns Hopkins Bloomberg School of Public Health, Executiv...